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TECHNICAL PAPERS

Two Transition Phase Control Methods for Hard Contact

[+] Author and Article Information
Nakju Lett Doh1

School of Electrical Engineering, Korea University, Seoul, Koreanakju@korea.ac.kr

Wan Kyun Chung

Robotics & Bio-Mechatronics Laboratory, Pohang University of Science and Technology, Pohang, Koreawkchung@postech.edu

Youngil Youm

Robotics & Bio-Mechatronics Laboratory, Pohang University of Science and Technology, Pohang, Koreayoum@postech.edu

Yongwhan Oh

 Intelligent Robot Research Center of Korea Institute of Science and Technology, Seoul, Koreaoyh@amadeus.kist.re.kr

1

Author to whom correspondence should be addressed.

J. Dyn. Sys., Meas., Control 129(3), 262-274 (Sep 18, 2006) (13 pages) doi:10.1115/1.2719766 History: Received July 18, 2003; Revised September 18, 2006

A hard contact is an impact that occurs when the robot contacts a stiff environment with a high velocity. In the pretransition phase of the hard contact, it is important to maintain stability while reducing succeeding force peaks and the duration time. For these purposes, we propose two control methods. One is a suppression controller that suppresses position rebounds in-between the impact time. The other is a flexible-damped joint with a joint damping controller. The flexible-damped joint is a new joint type designed to increase the hardware damping. It is controlled by a novel controller, called the joint damping controller, to enhance damping. The major advantage of the proposed methods is a guaranteed stability. The performance of the proposed methods is validated via several comparative experiments.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

A typical force plot of the hard contact, which consists of pretransition phase, transition phase, and steady state

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Figure 2

Photo of the POSTECH DD-ARM I

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Figure 3

Schematic diagrams of the 1-DOF robot for (a) a contact and (b) a noncontact case

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Figure 4

System model during a contact state

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Figure 5

An illustration of the suppression controller: (a) is the position, (b) is the velocity, and (c) is the control input of the system

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Figure 6

Suppressing actions for a kth position rebound. The subscript k denotes the kth rebound. ta,k,ts,k,tb,k,tc,k (ta,ts,tb,tc, for short) are starting, switching, zero velocity, and ending time of the kth rebound, respectively.

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Figure 7

Time notations for the stability proof

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Figure 8

Experimental results of three different controllers: (ac) the joint torque controller, (df) the PI force controller with velocity feedback, and (gi) the suppression controller. Here, (a,d,g) are force plots, (b,e,h) are force plots for a time window of 0.1s, and (c,f,i) are control inputs for the same time window.

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Figure 9

Suppression controlled responses for (a) a conventional impact to the rubber and (b) a hard contact to the steel

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Figure 10

PI force-controlled responses for (a) a conventional impact to the rubber and (b) a hard contact to the steel

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Figure 11

Force errors with a low-pass filtering during the steady state for (a) the suppression controller and (b) the PI force controller

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Figure 12

Shapes of control input of (a) the posi-cast controller and (b) the suppression controller

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Figure 13

Flexible-damped joint

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Figure 14

Schematic diagrams of the flexible-damped joint robot for (a) the contact case and (b) the noncontact case

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Figure 15

Response of PI force controller for (a) the rigid joint robot and (b) the flexible-damped joint robot

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Figure 16

Joint damping controller’s actions for (a) q̇m<0 and (b) q̇m⩾0

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Figure 17

Control inputs of the joint damping controller for the case when the velocity directions of the motor and the link are the same: (a) q̇m⩾0 and q̇l⩾0 and (b) q̇m<0 and q̇l<0

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Figure 18

Control inputs of the joint damping controller for the case when the velocity directions of the motor and the link are different: (a) q̇m⩾0 and q̇l<0 and (b) q̇m<0 and q̇l⩾0

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Figure 19

Experimental results of the joint torque controller for (ac) the rigid joint and (df) the flexible-damped joint. Here, (a,d) are force plots, (b,e) are force plots for a time window of 0.1s, and (c,f) are control inputs for the same time window.

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Figure 20

Experimental results of the PI force controller with velocity feedback for (ac) the rigid joint and (df) the flexible-damped joint. Here, (a,d) are force plots, (b,e) are force plots for a time window of 0.1s, and (c,f) are control inputs for the same time window.

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Figure 21

Experimental results of three different controllers: (ac) the joint torque controller, (df) the PI force controller with velocity feedback, and (gi) the joint damping controller. Here, (a,d,g) are force plots, (b,e,h) are force plots for a time window of 0.1s, and (c,f,i) are control inputs for the same time window.

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